Based on the non-isothermal transformation theory and non-steady state nucleatio n theory, a new method for calculating the continuous cooling transformation cur ve and the critical cooling rate of bulk metallic glass alloys is put forward in this paper. The continuous cooling transformation curves of Zr- and Pd-based al loys are calculated and the results are in good agreement with the experimental values. It is suggested that the method can be used to evaluate glass forming ab ility of alloy systems more effectively. In addition, the calculation results sh ow that the main factors effecting the critical cooling rate are the viscosity o f melt, nucleation barrier and critical volume fraction of the crystal, the crit ical cooling rate is reduced with the increase of the viscosity, nucleation barr ier and critical volume fraction of crystal.